Tokyo -LRB- CNN -RRB- -- An explosion on an oil tanker off the Japanese coast set off a huge fire Thursday and left the vessel 's captain missing .

Ships and aircraft battled the blaze on the Shoko Maru , a 998-ton tanker anchored about 5 kilometers -LRB- 3 miles -RRB- off the port of Himeji in western Japan , the coast guard said .

Rescuers have recovered seven members of the eight-person crew , the coast guard said , but the ship 's 64-year-old captain is still missing .

Four of the rescued crew remembers were seriously injured in the blast , the Himeji fire department said , and all seven of them were taken to hospitals after arriving in the port , which is about 75 kilometers -LRB- 45 miles -RRB- west of Osaka on the Seto Inland Sea .

The tanker was n't loaded when the blast went off Thursday morning , the coast guard said , reducing fears of a major environmental disaster .

Video footage showed water cannons dousing the stricken ship as large black plumes of smoke rose from a blaze roaring inside its body . Later images showed the tanker scorched , smoldering and listing to one side .

There was no immediate danger to other ships , as the tanker was located outside of the port facility , the coast guard said , adding that an exclusion zone was being set up around the damaged vessel .

The coast guard said it was still investigating the cause the explosion on the ship , which belongs to Shoho Shopping Co. Ltd , a company based in Hiroshima , Japan .

CNN 's Yoko Wakatsuki reported from Tokyo , and Jethro Mullen reported and wrote from Hong Kong .

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NEW : Four crew members were seriously injured in the explosion near the port of Himeji

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NEW : The 64-year-old captain of the ship remains missing , authorities say

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NEW : The tanker was n't loaded with oil when the blast hit , the coast guard says

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Ships and aircraft battled the blaze on the Shoko Maru , a 998-ton tanker